1. Field of the Invention
The present invention relates to an error correction system for detecting and correcting an error in data created in an optical disk, a magnetooptical disk or a communication path such as is used in satelite communication, by using a code, and more particularly to a detection and correction system for an error due to synchronization of data.
2. Related Background Art
Errors in digital data include an error due to the change of a bit from "0" to "1" or from "1" to "0", and an error due to the loss of a bit or insertion of a redundant bit.
In the following description, the error due to the change of a bit from "0" to "1" or from "1" to "0" is simply called an error, and a code for correcting such an error is simply called an error correction code. On the other hand, the error due to the loss of a bit or the insertion of a bit is called a synchronous error and a code for correcting such an error is called a synchronous error correction code.
Many studies have been made on error correction codes, and an excellent code for correcting a random error or a burst error has been proposed.
However, in a correction code based on the Hamming distance theory, if there is a loss of a bit or the insertion of a bit, all succeeding bits are shifted and all bits after the shift may be determined as an error. In such a case, the limit of error correction ability of the correction code is exceeded. Accordingly, effective correction is not made for a synchronous error.
In the past, the correction code has not been used for a synchronous error, but the occurrence of error has been prevented by frequent resynchronization.
A synchronous error is considered to take place when the synchronization of the clock for the data is shifted. Such an error may occur more frequently than a simple error depending on the communication system used. Frequent resynchronization can correct this but it considerably lowers the overall transmission efficiency.